Should be either 401 or 200 with proper error message.

Secondly, what are the instructions to run the service? Missing that in the README.

So far as a developer, I'm starting it using:

export SERVER_PORT=8081

java -jar -Dspring.profiles.active=local \
    ../notification-service/target/notification-service-1.0.4-SNAPSHOT.jar

and invoking by:

curl -X 'GET'  'http://localhost:8081/api/v1/notifications?page=0&size=1&sort=string' -H 'accept: /' -H 'Authorization: Basic dGVzdDp0ZXN0'